1. Field of the Invention
The invention relates to identification and preview of radiographic images that are stored in a photostimulable phosphor screen.
2. Background of the Invention
In the field of digital radiography a wide variety of image acquisition techniques have been developed that render a digital representation of a radiation image.
In one of these techniques a radiation image, for example an X-ray image of an object, is stored in a screen comprising a photostimulable phosphor such as one of the phosphors described in EP-A-503 702.
In a read out station the stored radiation image is read by scanning the screen with stimulating radiation such as laser light of the appropriate wavelength, detecting the light emitted upon stimulation and converting the emitted light into a digital signal representation that can be subjected to different kinds of image processing techniques.
The original or enhanced image can then be transmitted to a hard copy recorder for reproduction of the image on the film size and lay-out of the radiologist""s choice and/or it can be applied to a monitor for display.
It can also be processed and evaluated in an off-line review station and/or archived in an archive station.
After read-out the residual image left on the photostimulable phosphor screen is erased so that the screen is again available for exposure.
As in conventional radiography the radiographic image needs identification, i.e. it needs to be associated with a patient. Further, adjustment parameters for the components of the read out device as well as parameters to be used during image processing are to be defined and associated with the radiographic image.
The currently used identification system operates as follows.
A photostimulable phosphor screen is conveyed in a cassette that is provided with an EEPROM having a number of electrical contacts for power supply and read-write transfer of identification data.
The radiologist or operator performs a radiographic exposure of a phosphor screen in the cassette and feeds the exposed cassette into an identification station so that mechanical contact is made between the electrical contact points of the EEPROM on the cassette and contact pins in the identification station.
Then, the identification data of the patient are entered via keyboard into an identification program running on the identification station.
Alternatively, in case the identification station is connected to a hospital information system (HIS) or a radiology information system (RIS), the identification data can be retrieved from the RIS/HIS and entered automatically.
They can be retrieved via a file of known format transmitted over a computer link as has been described in EP-A-674 187.
Further, an examination type identifier is entered. This is performed by selecting a specific examination type (and subtype) out of a hierarchically popped up menu that is displayed on the screen of the identification station.
With an examination type identifier several settings for the read out apparatus, parameters to be used during image processing and parameters that relate to image reproduction etc. are linked. The set of settings and parameters was stored in advance in each of the stations where it is to be used according to a customisation procedure as has been described in EP-A-679 909.
Then, the patient identification data and the examination type identifier are written into the EEPROM on the exposed cassette.
Further details on this procedure as well as on the outlook of the cassette are described in U.S. Pat. No. 4,960,994.
The exposed and identified cassette is then fed into a read out station where the data stored in the EEPROM are read.
Next the radiographic image stored in the photostimulable phosphor screen is read taking into account the settings for the read out apparatus that correspond with the identifier read from the EEPROM.
The read out image is further subjected to processing taking into account the processing parameters corresponding with the identified examination type.
Next, the screen is erased and at least some of the data stored in the EEPROM are erased (or updated).
In an alternative embodiment such as the embodiment described in EP-A-727 696 the identification data are transferred from a dedicated identification terminal to a radiofrequency tag.
It is common practice to display a preview of the image that is read out from an exposed photostimulable phosphor screen before it is sent to a soft copy or hard copy station or to an archive station etc. The preview image is a low resolution version of the read out and processed image.
The preview gives the operator early feedback on the image quality and allows him to perform a further or a new exposure of the patient in case the image acquisition went wrong or in case the image does not correspond to his expectations.
Several aspects concerning a preview station have been described in EP-A-567 176.
The monitors that are used nowadays as preview monitor are VGA monitors connected via a coaxial cable with a read out apparatus. This implies that the distance between the apparatus where the digital image representation is generated (in case the read out apparatus), is limited and that also the number of monitors that can be connected to the read out system, is limited.
For this reason, a single central preview monitor is commonly used. This monitor is installed in the neighborhood of the read-out apparatus, which apparatus is normally placed outside the radiography rooms. The central preview monitor is then used for display of radiographic images taken in different radiography rooms but read out by the same read out apparatus.
This implies that in most cases an operator who wants to consult the preview monitor has to leave the radiography room and approach the preview monitor in order to wait for the image of his interest to be displayed so that he can evaluate it.
He thus has to leave his patient alone waiting in the radiography room until he has evaluated the image and has decided whether or not further images or retakes are required.
This is not a user-friendly solution.
It is an object of the present invention to provide a user-friendly preview system for use in the field of digital radiography using photostimulable phosphor screens as intermediary storage medium.
Further objects of this invention will become apparent from the description hereafter.
The above-mentioned objects are realised by a system for displaying a visual image of a radiation image that has been stored in a photostimulable phosphor screen comprising:
a personal computer having
means for entering data identifying said radiographic image and for displaying said data,
means for transferring said data onto an identifying means provided on a cassette conveying said photostimulable phosphor screen,
means for receiving a digital image representation of said radiographic image read from said screen and for displaying a visual image corresponding with said digital image representation.
The system of the present invention overcomes the disadvantages of the prior art.
A personal computer can be connected to the read out apparatus through an Ethernet connection so that the limitations which were implied by the use of a VGA monitor and coaxial cableconnection no longer exist.
In the system of the present invention the identification function and the preview function are combined on a single personal which is a more user-friendly embodiment.
In one embodiment the means for displaying a visual image are arranged for displaying a mosaic image composed of a number of successively read out images.
In this embodiment reduced image signals representing reduced images comprising less pixels than the original radiation image, are deduced from the digital image representation of the radiation image and a composed signal representing a mosaic type image is formed by means of a number of the reduced image signals.
The composed signal is then applied to a monitor.
In one embodiment, as a new reduced signal is deduced, the composed signal is amended by means of the new signal so that at least one of the reduced images in the displayed image is replaced by the image represented by said new reduced signal.
Preferably a first in, first out order is applied.
The reduced signal can be obtained by sub-sampling or interpolation.
Alternatively in case image processing is applied that is based on decomposition of an image into a multi-resolution representation, amendment of the multi-resolution representation and reconstruction as will be described in greater detail further on, the reduced image can be obtained as a low resolution approximation.
Still alternatively it can be an intermediate image obtained during reconstruction up to some intermediate resolution level.
Preferably a processed image of 1024 times 1024 pixels is calculated in the processing unit of the read-out station or in a separate processing station. This low resolution image is sent to the preview station where it is stored. The number of pixels in the image that is sent to the preview station is preferably 1024xc3x971024 because this number corresponds with the resolution of currently available display screens. However, this number can be configurated.
In the preview station a mosaic type image is composed. Different lay outs are available (as will be described further on). Composition of most of these lay-outs may require further resolution reduction which is then performed in the identification and preview station.
In a preferred implementation, the means for displaying identification data and the means for displaying a visual image are arranged to simultaneously display a screen comprising identification data and a screen comprising the visual image so that these screens partially cover one another.
In this way it is possible to perform identification of a patient without losing sight of the display of images that are provided by the readout apparatus.
In a specific embodiment the cassette conveying the photostimulable phosphor screen is provided with a radiofrequency tag. Radiofrequency tags are known in the art. These devices operate on the basis of data transfer by means of radiofrequencies emitted by an antenna connected e.g. to a personal computer. A Read/Write coil generates by magnetic induction a constant field strength that is sufficient to power the tag""s circuitry and the memory of the tag and to generate a system clock on the tag.
The means for transferring data onto an identifying means provided on a cassette conveying said photostimulable phosphor screen, are then adapted for transferring data through radiofrequency transmission.